This worked perfectly for me when I had the same problem:
Power management software in Windows Vista
Understanding battery charging issues
If the notebook battery is not charging or the notebook does not indicate that the battery is charging, the most likely scenario is that the battery itself is operating correctly, but its power management software may have become corrupt. In order to correct the problem, you will need to uninstall and reinstall the power management software by using the Device Manager. This document will explain how to uninstall and reinstall the ACPI Battery listings in Windows Vista, as well as how to obtain and install updated BIOS files, if needed to correct other battery issues.
Uninstalling and reinstalling power management software in Windows Vista
In order to correct problems with the battery's power management software, follow the steps below.
1. Click Start and type device in the search field, then select Device Manager .
2. Expand the Batteries category.
3. Under the Batteries category, right-click the Microsoft ACPI Compliant Control Method Battery listing, and select Uninstall .
WARNING: Do not remove the Microsoft AC Adapter driver or any other ACPI compliant driver.
4. On the Device Manager taskbar, click Scan for hardware changes .
Alternately, select Action > Scan for hardware changes .
Windows will scan your computer for hardware that doesn't have drivers installed, and will install the drivers needed to manage your battery's power. Restart your computer. The notebook should now indicate that the battery is charging.
